Performance Evaluation of a Gypsum-Based Desulfurizer for Sulfur Recovery from the Smelter Off-Gas: Experimental Analysis and Thermodynamic Performance

To find some new desulfurizers for the smelter off-gas containing high levels of SO2, both the sulfur recovery performance and the regeneration performance of the sulfides of alkali metals and alkaline-earth metals were compared in both simulation and experiment. Although sodium sulfide (Na2S) showed a good sulfur recovery performance, its regeneration performance was poor due to the production of polysulfides. Calcium sulfide (CaS) was a feasible option of the desulfurizer because both its sulfur recovery performance and regeneration performance were satisfactory. CaS was prepared after the reduction of the commercial CaSO4 (Red-Ca), the flue gas desulfurization gypsum (Red-FGD), the phosphogypsum (Red-P), and the titanogypsum (Red-Ti), respectively. The results showed that the performances of Red-Ca and Red-FGD were quite similar and both of them were distinctly better than Red-P and Red-Ti. According to XRF analysis and XRD patterns, the impurities in Red-P and Red-Ti reduced the activity of CaS. The sulfur recovery performance of both Red-FGD and Na2S in the presence of oxygen decreased comparing with the performance in the absence of oxygen, while the decrease for Red-FGD was less than Na2S. Higher reaction temperature and lower space velocity could significantly enhance the sulfur recovery performance of Red-FGD. The sulfur recovery performance was very stable in the investigated NO concentration, i.e., 400-800 ppm. SEM photos indicated that some mesopores newly occurred in the reduction of the FGD particles but then the porosity decreased to some extent after the desulfurization.